The present invention relates to an electric keyboard having snap contacts.
There are many keyboards in which the depression of a key leads to an electrical connection between two areas of a circuit effected by the snap action of metallic laminae. These laminae are very elastic and, for example, are given a bow-shaped or dome-shaped form. Each lamina is supported at the edges and depression of a key leads to the compression of the lamina through an intermediary spring. Its deformation into an unstable configuration leads to the sudden production of a curvature in the opposite direction to that present initially and to the formation of the desired electrical connection. On releasing the key the elasticity of the material overcomes the load of the intermediary spring and restores the lamina to its initial stable form.
Known keyboards of this type have the advantage of being economical. However, the working load of the key is found to be greater than that in the best release keyboards; besides this, the release behaviour of the individual key depends essentially on the physical and dimensional characteristics of the material employed for the lamina and on its processing, with particular reference to wear of the stamps used in manufacture. In order to ensure uniform ergonomic conditions of different keys in a keyboard, it is generally necessary to test the keys, which means a considerable increase in the cost of the keyboard. Finally, the present values of the working load exclude the use of these keyboards in sectors of typing machines and apparatus for data transmission where the ergonomic demands by users are very severe.